(a) Field of the Invention
The present invention relates to a base station and a mobile terminal for location detection, and a location detecting method. More specifically, the present invention relates to a base station and a mobile terminal for location detection, and a location detecting method using a GPS technique and dedicated short range communication (DSRC).
(b) Description of the Related Art
Methods for detecting locations of mobile terminals include a technique that decides a location of a base station having a cell ID as a location of a mobile terminal, an AOA (Arrival Of Angle) method by which a base station determines a location of a mobile terminal through a direction angle of a signal transmitted from the mobile terminal, and a TDOA (Time Difference Of Arrival) method that detects a location of a mobile terminal using a time difference of arrival of a signal between the mobile terminal and a base station. The location detecting methods further include a technique that detects a location of a mobile terminal through a combination of the AOA and TDOA methods, RF fingerprinting that compares an RF characteristic value of a signal received from a mobile terminal with a value stored in a database to detect a location of the mobile terminal, a technique using a global positioning system (GPS), and a network-assisted GPS method.
In the method using a GPS, a mobile terminal receives signal information of the GPS such that a location of the mobile terminal is detected.
This method is easy to use and can detect a relatively accurate location of the mobile terminal outdoors. However, it consumes a large amount of electric power, requires a long time to first fix (TTFF), and has many restrictions on location detection indoors and in downtown areas due to interference of multiple paths and an insufficient number of visible satellites.
With the network-assisted GPS method, which is one method for is solving the problems of the GPS method, a mobile terminal can be provided with assistant data required for obtaining a list of satellites and satellite signals from a base station to reduce the time to first fix and additionally receive a correction signal.
The method using a cell ID can easily detect a location of a mobile terminal without modifying the existing equipment. However, this method has a problem in that accuracy of a location detecting result varies with a cell diameter. For example, a macro-call has an error of approximately 20 Km in diameter, a micro-cell has an error of 0.5 to 1 Km in diameter, and a pico-cell has an error of about 50 m in diameter.
With the AOA method, a base station measures a direction angle of a signal transmitted from a mobile terminal using an array antenna to detect a location of- the mobile terminal. However, this technique has a large location error because it is difficult to secure LOS (Line Of Sight) due to a multi-path in downtown areas. Furthermore, since the AOA method requires an array antenna, the mobile terminal has difficulty in using the method.
The TDOA method calculates a distance between a mobile terminal and a base station using a one-way signal arrival time between the mobile terminal and base station. With this method, a final location of the mobile terminal is detected from intersecting points of circles having three base stations at their centers. However, this technique has poor location accuracy.
The RF fingerprinting is an auxiliary location detecting method used to detect a location of a mobile terminal in downtown areas or inside buildings where the method using a GPS is difficult to use. This technique should continuously update a database according to a geographical environment and a channel state. In addition, its location detection performance is deteriorated due to a plurality of mobile terminals.
As described above, conventional location detecting methods are divided into techniques using a GPS and techniques not using GPS.
The techniques using a GPS have geographical restrictions that require LOS to be secured, need a long time to first fix, and consume a large amount of electric power, although they can detect a location of a mobile terminal relatively easily.
To solve the aforementioned problems, the network assisted GPS method allows a mobile terminal to receive information required for GPS location detection from the nearest base station. Thus, this method can reduce time and power consumption required for location detection. A network based location detecting method is used in areas where GPS location detection is impossible, such as downtown areas or indoor areas. However, the network assisted GPS method has a problem in that a location detection error is increased depending on a cell area when a location of a mobile terminal is detected using a network.
Among the techniques not using GPS, the AOA method can be used only in a base station because it requires an array antenna. Furthermore, a location detection error is increased due to a multi-path effect in downtown areas. As a distance between a mobile terminal and the base station is increased, the location detection error is also increased.
The TDOA method generates an error caused by locations of base stations, an error due to a multi-path in downtown areas, an error caused by a near-far problem due to a high reception signal from a near base station, and so on.
Methods other than the above-described techniques also have restrictions on location detection with high accuracy.